Examples of the cooling curves obtained at three of the 8 positions along a specimen for which
cooling curves had been determined are given in Fig. 4. The curves in Fig. 4 initially have the same
form, indicating that the field had no significant influence on the cooling rate produced by the silicone
oil. However, a change in the curvature and form of the curves occurs at a critical temperature,
indicating an evolution of heat due to a phase change, namely austenite-to-pearlite. The beginning and
end temperatures of such changes in the cooling curves (e.g. points a, a9 and b, b9 on the curve for 5–6
mm) increased with distance from the quenched tip (i.e., with decrease in cooling rate) and were lower
with the field compared to without. To be noted is that the curve with the field for the position 3–4 mm
shows no change in form, indicating that essentially no pearlite had occurred. This was confirmed by
optical microscopy in that the microstructure consisted of ;100% martensite (Fig. 3b)